The observed activity of polyspermine-ribonuclease toward double-stranded substrates, including viral RNA's, is prompting the preparation of other cross-linked combinations. SH-Groups are being introduced into RNase to yield, after oxidation, a dimer cross-linked by -S-S- bonds, to simulate the structure that occurs in the RNase in bovine seminal plasma. Work is in progress on the cross-linking of RNase and DNase to study the action of the product on hybrid substrates. With a method for the preparation of the RNase inhibitor from human placenta in stable form at hand, the method is being applied to beef liver as a source of the inhibitor in ability of the inhibitor will permit study of its effectiveness, as a biochemical reagent, increasing yields of protein biosynthesis in in vitro translation and transcription studies, where endogenous neutral RNase can be a source of interference. Experiments on the antitumor action of RNase dimers are being extended to the attachment of galactose residues to the enzyme with a view of increasing the specificity of the agent for the liver.